Mixture for the production of a high-expansion stone die

ABSTRACT

The present invention refers to a mixture comprising alpha CaSO 4 ×½H 2 O, CaSO 4 ×2H 2 O, a combination of a hardening accelerator, a hardening retarder and a setting expansion inhibitor, and optionally a surfactant.  
     The mixture can be used to prepare a die having an extremely high setting expansion.

[0001] The present invention relates to a mixture for the production ofa die.

[0002] In recent times dental implants, bridges and crowns were preparedusing gold since gold has superior properties and can be processed quiteeasily. Today, people require ceramic materials for aesthetic reasons.However, processing of ceramic material is quite complex and requires alot of time and work so that new improved techniques are needed toprocess ceramic materials more effectively.

[0003] When producing ceramic implants, crowns or bridges, a model(master model) of the tooth to be covered with the ceramic material isprepared. Then the master model is duplicated with a die material likegypsum or plaster as disclosed in the book “Gips . . . und was mandarüber wissen sollte” (Martin Kuske & Ralf Suckert—teamwork media—2000)especially chapter 1, page 18 ff. Known dental plasters are dividedaccording to the norm DIN/EN 26873 IS 6873 into five types: SettingCompression strength in Mpa Type Expansion % min max I   0 to 0.15 4 4II   0 to 0.30 9 — III   0 to 0.20 20 — IV   0 to 0.15 35 — V 0.16 to0.30 35 —

[0004] Such plasters have a setting expansion of at most 0, 3%. The die,produced with this kind of plaster, is covered with a ceramic suspensionto build a ceramic cap (also called green body before the sinteringprocess) and then the covered die is dried at temperatures of about 900°C. In a second step, die and cap are separated and the ceramic cap isheated (sintered) to about 1400 to 1500° C. At such temperatures theceramic material of the cap shrinks to an extent of from about 4% up to12%. Accordingly, the cap is too small and does not fit on the patient'stooth so that the ceramic cap has to be adapted to the tooth by removingceramic material. Repeatedly, the fit of the cap on the tooth is testedand excess material removed until a good fit has been achieved. Thisprocedure is time-consuming, expensive and inconvenient for the patient.

[0005] In order to overcome this disadvantage it has been proposed toprovide a die material which expands during setting. If such material isused, the die material and accordingly the ceramic material covering thedie would have a too big/loose fit in a pre-sintered stage so that agood fit of the final sintered ceramic cap to the tooth would beachieved. However, no such material is available: As mentioned above,currently available plaster has a setting expansion of up to 0.3% whichis far from satisfactory.

[0006] It was accordingly an object of the present invention to providea material which overcomes this disadvantage of the prior art.

[0007] It was especially an object of the present invention to provide adie material which expands to an extent that the shrinkage of a ceramiccap can be neutralized. Thus, a die which consists of such material canbe used for the production of a ceramic cap which needs no furthermodification and fits exactly onto a patient's tooth.

[0008] This object has been achieved according to the present inventionby providing a mixture, comprising:

[0009] a) 100 parts by weight αCaSO₄ ×½H ₂O,

[0010] b) 1-20 parts by weight CaSO₄×2H₂O,

[0011] c) 0.005-0.80 parts by weight of at least one additive and

[0012] d) up to 2 parts by weight of one or more surfactants.

[0013] This mixture can further comprise

[0014] e) 15-65, preferably

[0015] 23-45 parts by weight of a liquid such as water or a colloidalsilica suspension.

[0016] The mixtures according to the present invention can be used toprepare a die which has a setting expansion of about 4 to about 14%.When such a die is covered with a ceramic material and heated to, e.g.,about 900° C., the die and accordingly the ceramic material expand to acorresponding degree. When the ceramic cap is then removed from the dieand fired at a temperature of, e.g. 1400° C. to 1500° C. the ceramicmaterial shrinks to its original size so that the cap fits exactly tothe patients tooth.

[0017] Some or all components a), b), c) and optionally d) and/or e)will usually be provided in separate containers as a kit of parts sothat the dentist or the dental laboratory can combine them in anyappropriate ratio. It is also possible to provide a mixture ofcomponents a)-c) and optionally d) with a defined expansion ratio. Thismixture can be mixed with water in a recommended ratio. Alternativelycomponent e) can be provided in a predetermined amount, again resultingin a specific expansion of the die when all components are mixed.

[0018] According to one embodiment of the present invention, a die canbe produced by mixing components a) to c) and e) and optionally one ormore of components d), preferably while stirring the mixture. Accordingto this embodiment, the material is then poured into a mold which is anexact negative of the patient's tooth to be treated. Care should betaken at this stage to avoid voids in the die; if voids are formed at asurface of the die, protrusions will be formed on the cap which willhave to be removed during further work-up. If voids are formed withinthe die, the die will not be homogenous thereby preventing a linearexpansion of the die. This also results in a cap which must be worked-upwith considerable difficulty. Methods to prevent formations of voids ina die are known in the art and should accordingly be applied in thepresent case.

[0019] When the die has hardened to a degree that it can be handledwithout being damaged, it is covered with a ceramic cap e.g. by dippingthe die into ceramic material, drying the ceramic material and repeatingthese steps until the required strength and size of the ceramic cap hasbeen achieved. The materials are then heated to a temperature of e.g.about 900° C. During this heating step, the die expands to the requireddegree, thereby co-expanding the ceramic cap. The cap is then removedfrom the die and heated to a temperature of about 1400 to about 1500° C.During this sintering step, the cap shrinks depending upon the ceramicmaterial used, e.g. by about 13%, thereby regaining the required size.

[0020] A further advantage of the present invention is that theproperties, especially the expansion of the die can be varied to a largeextent: If the ceramic material used for the production of a cap has aspecific shrinkage, the mixture according to the present invention canbe adapted so that the die expands to exactly meet this shrinkage.

[0021] There are a number of factors which influence the properties suchas setting and thermal expansion and compressive strength of the die.All solid materials used in the present invention are preferablyemployed as powders or fine grains. They can e.g. have an averageparticle size of about 3 μm to about 70 μm.

[0022] 1. The type of the αCaSO₄×1/2H₂O a):

[0023] An important factor is the quality and type of the αCaSO₄×1/2H₂Oto be used. Basically any a gypsum hemi-hydrate or any mixture thereofcan be used. Examples are synthetic gypsum T, natural gypsum K andnatural gypsum PL, all of which are commercially available. If syntheticgypsum T is used, the expansion of the resulting die is larger than whennatural gypsum K or natural gypsum PL are used, please compare withTable 1.

[0024] 2. The amount and the type of the CaSO₄×2H₂O b):

[0025] A further important factor is the quality and type of thedihydrate to be used. Basically any dihydrate and any commerciallyavailable dihydrate can be used.

[0026] Moreover, the amount of the dihydrate to be added to the mixturehas a large influence on the properties of the resulting die. As can betaken from table 2 an increase from 2 parts by weight to 10 parts byweight increases the expansion from 3-4% to 11-12%. The dihydrate can beused in amounts of about 1-20 parts by weight, while 2-15 parts byweight are preferred. As mentioned above, the amount will be determineddepending on the requested properties of the die.

[0027] 3. The Amount and the Type of Additives c):

[0028] The mixture according to the present invention can comprise one,two or more additives. Examples of such additives are hardeningaccelerators, hardening retarders, and setting expansion inhibitors.Such components are described in e.g. Skinner's Science of DentalMaterials, Ralph W. Phillips, 1982, 8^(th) edition.

[0029] For example, as the hardening retarder(s), carboxylates (citrate,succinate, . . . etc) and water soluble high polymers (cane sugar,hexameta phosphate, . . . etc) can be used in the present invention.Preferably tri sodium citrate is used.

[0030] For example, as the hardening accelerator(s) inorganic acid salts(sodium chloride, potassium sulfate, . . . etc) may be used in thepresent invention. Preferably potassium sulfate is used.

[0031] For example, as the setting expansion inhibitor potassium saltsand sodium salts etc. (potassium chloride, potassium tartrate, potassiumsodium, sodium tartrate, . . . etc) can be used in the presentinvention. Preferably potassium tartrate is used.

[0032] Depending on the amount and combination of the additives, thephysical properties such as setting time, setting expansion andcompressive strength of the die can be varied, please refer to table 2.The amount of these additives can vary from 0.005 to 0.8 parts byweight, whereas a range of 0.01 to 0.4 parts by weight is preferred. Oneor a mixture of two or more additives can be used.

[0033] 4. The Amount and the Type of Surfactant d):

[0034] Especially a water reducing agent and/or dispersing agent can beused as a surfactant. Such agents are, for example,

[0035] anionic surfactants like alkylbenzene sulfonate, alkylnaphthalenesulfonate,

[0036]  a mixture of naphtalene sulfonates and formaldehydepolycondensation products,

[0037]  a mixture of melamin sulfonates and formaldehydepolycondensation products, dialkyl sulfosuccinates, alkylsulfonates,

[0038]  alpha-olefin sulfonates, sodium N-acyl methyl taurate,

[0039] nonionic surfactants like polyethylene alkylether,polyoxyethylene sec-alcohol ether,

[0040]  polyethylene polyoxypropylene alkylether,

[0041] polyglyceryl fatty acid ester.

[0042] An especially preferred surfactant is a mixture of melaminsulfonates and formaldehyd polycondensation products.

[0043] One function of the surfactant is to reduce the amount of liquidrequired for mixing and to increase the setting expansion. Commerciallyavailable surfactants are e.g. Pozzolith NR. 70, NR. 81 MP, NR. NL-1440or NR. NL-4000.

[0044] The surfactants can be used in amounts of up to 2 parts byweight, while amounts of 0.2 to 1 parts by weight are preferred. It is,however, possible to omit the surfactants altogether. Moreover, one or amixture of two or more surfactants can be used.

[0045] 5. The Amount and the Type of the Liquid e) to be Used:

[0046] The liquid(s) which can be used also can have an importantinfluence on the properties and especially the setting expansion of thedie. Preferably, a colloidal silica suspension is used. Commerciallyavailable examples are e.g. Levasil (Bayer) 100/45%, 200/40%, LUDOX(Dupont) H540, W30, W50.

[0047] The colloidal silica suspension is usually diluted to aconcentration of about 20 to 50 weight-% using distilled or tap water.Alternatively, distilled or tap water can be used as the liquid.Preferred amounts of the liquid to be added to the mixture of componentsa)-c) and optionally component(s) d) are 23 to 45 g liquid per 100 g ofthe mixture.

[0048] Thus, by varying the quality and/or the quantity of the abovecomponents, the properties and especially the expansion of the die canbe adapted. For example, the shrinkage of a desired ceramic material canbe determined and then a specific die can be selected based on theteaching of the present invention which has the appropriate shrinkage.

[0049] The present invention furthermore discloses a kit of partsespecially for dental purposes, containing at least components a), b)and c) preferably each in separate containers. Additionally it cancontain component(s) d), also in (a) separate container(s).

[0050] The components can be provided in pre-determined quantities andqualities so that a die material with specific properties such asexpansion etc. can be prepared in a dental laboratory by the dentist ortechnician.

EXAMPLES

[0051] Examples of compositions of the present invention are describedin the following tables.

[0052] (Instruction for Use)

[0053] Powder (components a), b), c) and optionally d))/Liquid ratio:

[0054] about 100 g/23 g-459

[0055] Hand mix powder into liquid for 15 seconds.

[0056] Blend to a homogenous mixture.

[0057] Pour into mold, especially a duplicate impression.

[0058] Bench setting for 10 minutes.

[0059] After 10 minutes remove from impression and put into water fortotal setting time (EX 2 hours) to get available setting expansion.TABLE 1 The difference of α CaSO₄ 1/2H₂O EX 1 EX 2 EX 3 (Weight (Weight(Weight (Composition) ratio) ratio) ratio) α CaSO₄ 1/2H₂O SyntheticNatural Natural gypsum gypsum gypsum T K PL 100 100 100 CaSO₄ 2H₂O 10 1010 Surfactant: a mixture of 0.2 0.2 0.2 melaminsulfonate and aformaldehyde polycondensation product Hardening retarder: 0.1 0.1 0.1tri sodium citrate Hardening accelerator: 0 0 0 potassium sulfateSetting expansion inhibitor: 0 0 0 potassium tartrate (Physicalproperties) Liquid concentration 40% 40% 40% Liquid / Powder ratio 28g/100 g 31 g/100 g 32 g/100 g Setting time (ISO) 8′00″ 10′00″ 11′00″Setting Iso/2 hrs More More More expansion than 4% than 3% than 3% Inwater/2 hrs 11.0˜11.5% 7.0˜7.5% 7.0˜7.5% Compressive ISO/1 hr 50 Mpa 50Mpa 50 Mpa strength In water/2 hrs 30 Mpa 30 Mpa 30 Mpa

[0060] TABLE 2 The difference of additives(1) EX 1 EX 2 EX 3 EX 4 EX 5EX 6 (Composition) (Weight ratio) (Weight ratio) (Weight ratio) (Weightratio) (Weight ratio) (Weight ratio) α CaSO₄ 1/2H₂0 100 100 100 100 100100 CaSO₄ 2H₂0 2 10 15 10 10 10 Surfactant: a mixture of 0.2 0.2 0.2 01.0 2.0 melaminsulfonate and a formaldehyde polycondensation productHardening retarder: 0.005˜0.05 0.06˜0.10 0.10˜0.20 0.06˜0.10 0.06˜0.100.06˜0.10 tri sodium citrate Hardening accelerator: 0 0 0 0 0 0potassium sulfate Setting expansion 0 0 0 0 0 0 inhibitor: potassiumtartrate (Physical properties) 0 0 0 0 0 0 Liquid concentration 40% 40%40% 40% 40% 40% Liquid/Powder ratio 28 g/100 g 28 g/100 g 28 g/100 g 28g/100 g 28 g/100 g 28 g/100 g Setting time (ISO) 3′00″˜10′00″5′00″˜10′00″ 5′00″˜10′00″ 6′00″˜11′00″ 5′00″˜10′00″ 2′30″˜5′00″ SettingIso/2 hrs — — — — — — expansion In water/2 hrs 3%˜4% 11%˜12% 10%˜11%10%˜11% 11%˜12% 12%˜13% Com- ISO/1 hr 50 Mpa 50 Mpa 50 Mpa 50 Mpa 50 Mpa50 Mpa pressive In water/2 hrs 30 Mpa 30 Mpa 30 Mpa 30 Mpa 30 Mpa 30 Mpastrength

[0061] TABLE 3 The difference of additives(2) EX 1 EX 2 EX 3 EX 4 EX 5EX 6 (Composition) (Weight ratio) (Weight ratio) (Weight ratio) (Weightratio) (Weight ratio) (Weight ratio) α CaSO₄ 1/2H₂O 100 100 100 100 100100 CaSO₄ 2H₂O 10 10 10 10 10 10 Surfactant: a mixture of 0.2 0.2 0.20.2 0.2 0.2 melaminsulfonate and a formaldehyde polycondensation productHardening retarder: 0.06˜0.10 0.06˜0.10 0.06˜0.10 0.06˜0.10 0.06˜0.100.10˜0.40 tri sodium citrate Hardening accelerator: 0 0.1 0.2 0 0 0.2potassium sulfate Setting expansion 0 0 0 0.1 0.2 0.2 inhibitor:potassium tartrate (Physical properties) Liquid concentration 40% 40%40% 40% 40% 40% Liquid/Powder ratio 28 g/100 g 28 g/100 g 28 g/100 g 28g/100 g 28 g/100 g 28 g/100 g Setting time (ISO) 5′00″˜10′00″4′00″˜8′00″ 2′30″˜6′00″ 4′00″˜8′00″ 2′00″˜6′00″ 3′00″˜9′00″ SettingIso/2 hrs — — — — — — expansion In water/2 hrs 11%˜12% 10%˜11% 8%˜9%8%˜9% 6%˜7% 3%˜4% Compressive ISO/1 hr 50 Mpa 50 Mpa 50 Mpa 50 Mpa 50Mpa 50 Mpa strength In water/2 hrs 30 Npa 30 Mpa 30 Mpa 30 Mpa 30 Mpa 30Mpa

[0062] TABLE 4 The difference of liquid and Liquid/Powder ratio EX 1 EX2 EX 3 EX 4 EX 5 (Composition) (Weight ratio) (Weight ratio) (Weightratio) (Weight ratio) (Weight ratio) α CaSO₄ 1/2H₂O 100 100 100 100 100CaSO₄ 2H₂O 10 10 10 10 10 Surfactant: a mixture of 0.2 0.2 0.2 0.2 0.2melaminsulfonate and a formaldehyde polycondensation product Hardeningretarder: 0.1 0.1 0.1 0.1 0.1 tri sodium citrate Hardening accelerator:0 0 0 0 0 potassium sulfate Setting expansion inhibitor: 0 0 0 0 0potassium tartrate (Physical properties) 0 0 0 0 0 Liquid concentration20% 40% 50% 40% 40% Liquid/Powder ratio 28 g/100 g 28 g/100 g 28 g/100 g23 g/100 g 45 g/J.OO g Setting time (ISO) 10′00″ 8′00″ 6′30″ 4′00″13′00″ Flow (ISO) 38 33 29 25 60 Setting Iso/2 hrs — — — — — expansionIn water/2 hrs  6% 11% 12% 13%  7% Compressive ISO/1 hr 50 Mpa 50 Mpa 50Mpa 50 Mpa 50 Mpa strength In water/2 hrs 30 Mpa 30 Mpa 30 Mpa 30 Mpa 30Mpa

1. Mixture, comprising: a) 100 parts by weight alpha CaSO₄ ×½H ₂O, b)1-20 parts by weight CaSO₄×2H₂O, c) 0.005-0.8 parts by weight of atleast one additive, and d) up to 2 parts by weight of one or twodifferent surfactants.
 2. Mixture according to claim 1, furthercomprising: e) 15-65 parts by weight of a liquid, such as water or acolloidal silica suspension.
 3. Mixture according to any one of thepreceding claims, characterized by b) 2-15 parts by weight CaSO₄×2H₂O.4. Mixture according to any one of the preceding claims, characterizedin that the at least one additive c) is a hardening accelerator, ahardening retarder or a setting expansion inhibitor.
 5. Mixtureaccording to any one of the preceding claims, characterized in that thehardening accelerator c) is selected from inorganic acid salts likesodium chloride and potassium sulfate, and the hardening retarder c) isselected from carboxylates like citrates, succinates, acetates andphosphates, and borates like borax, water soluble high polymers likecane sugar, hexameta phosphate, etylenediamine tetra acetate, starch,gum arabic, carboxymethyl cellulose and sugar alcohol, and the settingexpansion inhibitor c) is selected from potassium chloride, potassiumtartrate, potassium sodium, and sodium tartrate.
 6. Mixture according toany one of the preceding claims, characterized in that the surfactantsd) are selected from anionic surfactants like alkylbenzene sulfonates,alkylnaphthalene sulfonates, a mixture of naphthalene sulfonates andformaldehyde polycondensation products, a mixture of melamin sulfonatesand formaldehyde polycondensation products, dialkylsulfosuccinates,alkylsulfoacetates, alpha-olefin sulfonates, sodium N-acyl methyltaurates, and nonionic surfactants like polyethylene alkylethers,polyoxyethylene sec-alcoholethers, polyethylene polyoxypropylenealkylethers, and polyglyceryl fatty acid esters.
 7. Mixture according toany one of claims 2 to 6, characterized in that colloidal silicasuspension has a concentration of 20-50 wt.-%.
 8. Kit of parts,containing components a), b) and c) and optionally components d) and/ore) according to any one of the preceding claims in separate containers.9. Die, obtainable by using a mixture or a kit of parts according to anyone of the preceding claims.